Hi,Can someone enlighten me on how the engine start switches should be used to follow IRL procedures. I know you use GRD to start the engines when you're on the ground and the switches then returns to their OFF positions and I think you use FLT if you end up in a situation where you have to start up an engine during flight? But what about the CONT position, when should that be used? Also, which engine should you start first when on the ground - differs between different airlines? And does it happen that you start up both engines at the same time having the IGN knob in it's BOTH position and if not, why is there a BOTH position in the first place?Lots of questions :-) Thanks in advance for any answers!

Hi, Richard-I'll give it a shot:>I know you use GRD to>start the engines when you're on the ground and the switches>then returns to their OFF positions and I think you use FLT if>you end up in a situation where you have to start up an engine>during flight? I believe this is correct.>But what about the CONT position, when should>that be used?CONT is used during takeoff and landing to run the ignition continuously to reduce the potential for flameout. I think you switch to CONT just before the takeoff roll and to OFF after takeoff, and again during final approach and OFF after landing.>Also, which engine should you start first when>on the ground - differs between different airlines?AFAIK it's airline policy. I always go left-right, but I don't know if it matters.>And does>it happen that you start up both engines at the same time>having the IGN knob in it's BOTH position and if not, why is>there a BOTH position in the first place?You never start both engines at the same time (I don't know if it's even possible IRL- not enough bleed air pressure, although this might depend on the model). The L, R, and BOTH refers to which ignition in each engine is used to start (there are two in each engine). On L, the left ignition in each engine is used to start, etc. You're supposed to alternate between flights to even the wear on the ignitions- as far as I know, BOTH is only used in the event of an emergency start in the air.Hope this helps (and that I'm close to the truth!).-Simon Binder

To add to what Simon has already said:The CONT setting will continously energize the _selected_ igniter. (That's the knob with L, Both, R). CONT should be used during all takeoffs, all landings, operations during heavy turbulence and or high moisture to avoid flameout as Simon correctly said.The FLT setting will continously energize both igniters, regardless of the selected igniter. (There is no difference between CONT and FLT if you select both igniters!). FLT is used during restarts in the air, but only if the engine is windmilling fast enough as the start valves will not open. If you do need bleed air to start the aircraft in the air, you have to use GND.As to engine start sequence, usually the right engine is started first. This is not a requirement, just a carry-on from turboprop aircraft. On turbopropos, usually the right engine is started first as the cables running from the BATT to the right engine are shorter than the cables to left engine and therefore have slightly more power to start it.Regards,Mark

Thanks alot both Simon and Mark for your replies!

I think that the order of which engine is started has to do with what that engine powers too. On the 747, I think engine 4 starts first because it drives the hydraulics for the brakes, then 1, 2 and 3. Not sure if this matters on the 737.Also, while I can't test this atm, I think the position of the ignition switch doesn't really matter in the sim to start engines as modeled, so you can start engine 2 with the ignitor set for 1.

Regarding the igniter, again, this has got nothing to do with engine 1 or engine 2. Both engines have 2 igniters. A left one and a right one. Selecting the right igniter energizes the right igniter in engine 1 and the right igniter in engine 2!Regarding start up:there are many ways you can do this. You could power up hydraulics with the electric pumps to supply the brakes. You also still have the accumulator!In the 737 there is a small thing you should observe:For pushback, the nose wheel steering has to be disabled. Some 737's don't have an override - you have to make sure hydraulic system A is not pressurized. This means, when starting engine 1, the engine driven pump and the eletric pump aswell have to be off . But that's not all: the solenoid which inhibits the engine pump from producing pressure, requires electric power to operate. A loss of electric power will open the valve and the pump will supply pressure. Therefore you are not allowed to connect the generators during startup as when you activate a generator, it trips the current generator, leaving the aircraft without power for a fraction of a second. This may be enough to open the hydraulic valve and pressurize system A, destroying the nose wheel steering!!Strange aircraft isn't it!Regards,Mark

Just to clarify - the ignition switch (L/Both/R) refers to the _igniters_ contained within an engine, not the L and R engines themselves (i.e. each engine has a L and R ignitor).So, the aircraft model is correct.- Bill(Edit: This is redundant info - Mark beat me to the punch!)

Excellent info Mark! I've always wondered about the igniter switch.As for startup sequence, I had no idea about the battery cables. I've always started the right engine first for a much more unrealistic reason .... the right starter switch is closest to the beacon light switch! (heh ... just kidding, I've always been in the habit of starting the right engine first due to turboprops ... the pax door is in front of the left engine, so it gets started last.)However, I do seem to remember reading somewhere that the engine start sequence is determined by which side of the aircraft the baggage doors are on, to accommodate last-minute baggage loading. I've never used the doors on the 737 so I'm not sure. I'll have to check when I get home. Either way, seems kinda odd, since you wouldn't normally start the engines until after pushback, right? (And thus the baggage doors would be locked up.)

I'll put my two peneth worth in now I suppose:Engine Start switches are used in the following manner:GRD for starting using bleed air (always on ground and sometimes in an relight situation if N2 is low)CONT used for continuous ignition, these are selected to CONT for T/O on ebetering the runway for take off as part of the pre-take off flow. Then selected OFF as part of the after take off flow (assuming eng anti ice not in use)During approach they are selected to CONT as part of the approach check flow then OFF after landing as part of the after landing flow.CONT is also selected at any time when ENG ANTI ICE is in use. The CONT setting should be selected BEFORE eng anti ice is turned on and turned off AFTER engine anti-ice in order to prevent ice ingestion and flameout!FLT is as stated where both igntion systems are energised and is the same as the ignition switch being in BOTH and the CONT setting being selected.The Ignition switch should be RIGHT for the first flight of the day (ie when leaving base). This is because the right system is powered by the Standby bus. If you cawnnot start in the right igntition system on the ground then you know that should an engine flame out in flight and you are on standby power then you cannot relight it!! This is a bad situation !Engine start sequence is normally 2 then 1, this is because you can start 2 and still be barding passengers through the main entry doors on the left. In a situation where you have no APU and so must use a ground air cart for bleed air you would need to start 1 first as the ground air cart socket is rather close to the eng2 exhaust . In this situation you start 1 then ask for the cart to be removed then do a crossbleed start on the number 2 using bleed air from the running number 1. Once starting is finished touch nothing until you see the man with the bypass pin waving as this means all persons are clear of the aircraft. At this point you can go through the after start flow (generators on, Pitot heat on, Pressurisation switch to FLT (not on NG), APU to off as required) . Should you select the generators on this can cause a spike in the system and provide power to the hydraulics and possibly cause injury to anyone working around the nosewheel. Hope that clears things upKris

Hi Kris,The kind of replies I got to my initial question in this thread is what makes this forum so fun and interesting to be in, thanks Kris and everyone else!

"Should you select the generators on this can cause a spike in the system and provide power to the hydraulics and possibly cause injury to anyone working around the nosewheel."Not sure I understand the logic behind this, Kris. What dangers are there around the nosewheel area? Are you worried about the nosewheel steering moving? I understand that some 737NG Standby Hydraulic Systems go through a self test when elec power is applied to the aircraft, but wouldn't hydraulics already be up and running when you start the engines? Or do you manually deselect all the hydraulics systems off because your particular airline's 737's are not fitted with steering bypass pins?Notwithstanding, the Standby Power system doesn't power the Nosewheel Steering, does it? Thanks.Cheers.Ian (Rookie 737NG engineer).

Hi Ian,Just on Kris' behalf.If you should get a burst of HYD pressure to the nosewheel steering system and the nosewheel is not aligned with the Tiller on the flightdeck then it will try and move to the commanded position.. now it may have a towbar and great big mothering tug connected to it which might just break something or worse it may only have the towbar connected to it and the HYD system is more than enough to flick that around fast enough to do serious damage to anything it strikes.The Nosewheel Steering Bypass Pin should prevent all this when inserted however.Rgds,

Thanks Brad, got in before me! Thats exactly the reason!Kris

Not sure if you've caught my drift guys... Perhaps I didn't explain myself properly.... The engines have already been started... Engine-driven hydraulic pumps are already pumping out 3000psi to both hydraulic systems. Surely, switching off and on weaker powered electric pumps is not going to make the hydraulics do anything more than they were before. If your hand is pushing/pulling on the tiller with the engines running, you've already broken the towbar... and my legs.Or have I missed something?Cheers.Ian.

Hi Ian,Nose Wheel Steering Bypass pin MUST be installed or BOTH System A HYD Pumps must be off when towbar etc connected. This is job of Engineer to both fit and remove the pin.This better? Sorry if I didn't explain well in first instance.Rgds,